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What's the appropriate course of action if an airliner bounces 5-10 feet on touchdown?
I regularly fly in a PC flight simulator, and I'm currently trying to refine landings in medium-to-large airliners in various weather conditions.
A problem I've faced in some conditions while flying the 737-800 has been bouncing on touchdown, where I lose just enough lift in the last few feet of my approach to touch down firmly on the main gear only, before bouncing back up 5-10 feet.
While I'm already looking into avoiding this kind of bounce whenever possible, I'd like to know what common procedures are in this situation assuming the gear is left intact and there's no urgent failures or factors (such as a fuel emergency) which would time-constrain a landing. Specifically; would a real-world flight in this situation go around, adjust thrust, adjust flare, or do something else entirely?

5-10 feet, you're probably going too fast, and the bounce is more of a "refusal to stop floating"...

You might want to read up on FedEx Flight 14 and FedEx Flight 80.

MD-11 is notoriously famous for its flight characteristics if bounced. It should not be considered a common example when discussing a bounced landing.

The dynamics affecting the aircraft during the seconds surrounding touchdown are fairly complicated (e.g. ground effect, landing gear strut damping, airframe structural modes). PC simulators typically do not model these accurately.

in addition to what @pericynthion states, many PC flight simulator flyers tend to focus too much on making silky smooth landings, often ending up floating a lot and then forcing themselves down hard when they notice they're not touching down normally. An airliner should land firmly but gently, so with enough vertical speed to stay put but not enough to cause damage or bouncing. Forget about that 1m/s touchdown speed, 100 is fine :)

If I bounced that high, my course of action would probably involve a fresh set of underwear.

Well, "5 to 10 feet" is not "slightly."  One or two feet is "slightly," and in that case you can maintain your landing attitude or pitch very slightly nose-down -- really a matter of the slightest change in pressure, not really a perceptible change in pitch -- and you'll land soon after that.
However, for a larger bounce, the concern, especially on the longer 737's, the -800 and -900 and -900ER, is a tail-strike. The tail skid protects the tail from a strike on takeoff, but on landing the geometry is different and the skid won't be what contacts the runway; it will be the fuselage.  And while tail strikes on takeoff are more common, it's the tail strikes on landing that are far more damaging & expensive. So avoiding one of those is a major concern.  Thus, the usual guidance in the event of a bounced landing in the 737-800 is not to attempt to salvage the landing, but rather to go around.  You may touch down again during the go-around, and that's okay, but you're better off aborting the landing & taking it around to try again, than to risk damaging the aircraft by trying to recover from a high bounce.
One thing that complicates recovering from a bounce is the fact that your spoilers may have extended when you touched down the first time -- and the last ten feet to the runway with spoilers fully extended & power already at idle, won't look nearly the same as the usual last ten feet to the runway, with power coming off & no spoilers. You'll settle fast, and hard, and you won't have the elevator authority you're used to for adjusting the sink rate.  You can pull back, but the change in attitude probably won't arrest the sink rate the way you think it will -- you'll just hit harder & in a more nose-high attitude.  Thus the increased risk of hitting the tail.
On a shorter aircraft without the tail-strike concerns (say a 737-200,  -300, -500, -600, or -700), it might be possible to salvage the bounced landing, although 10 feet up is a pretty high bounce -- even if you had a lot of airspeed to play with and runway ahead of you, I'm not sure it would be wise trying to sort that situation out -- go around & try again.

Your first reaction should be to advance the throttles. Not all the way, but to around 40%. This keeps the plane flying and avoid it sinking onto the ground in an impact that might collapse the landing gear.
Your second instinct would be to avoid large or abrupt pitch changes. If you attempt to chase it, you might end up in pilot-induced oscillations. Forget about the VSI and radar altimeter, fly the AI. Pitch to about 2~3 degrees up.
That is why you always have one hand on the throttles and the other hand on the yoke while landing.

Now that you have accomplished all that, you can evaluate your options. What is the condition that caused the bounce? Is there a strong and gusty crosswind? Poor height judgment? Excessive airspeed? How likely is it that you can land it on the remaining runway? Are you trying to land on a 13,000 feet runway on a calm day, or 7,500 feet runway on a rainy night?
You need to make a decision quickly. Ralph J has already stated the things that can go wrong when you try to salvage a bounced landing, which I will not repeat here.
Also, as stated, a bounce to 10 feet in real life is a very hard bounce, and more than a few passengers will certainly be upset. Unless there is an emergency or fuel situation, a go-around is always an option. And the reason why pilots have license is to ensure they won't end up going-around every time until they run out of fuel.

Glad you addressed the general case.

I that case, you just have to keep the nose up at the same angle and you don't touch anything... Just wait to be back on the ground.
This is the safest way because :

if you put more engine power at this particular moment you will perform a very long landing and it's not safe at all.
If you try to pull the nose up, you"ll risk to touch the tail.

To avoid to rebound, try to wait until 10 to 20 feet on a 737 (30 to 40 feet on a B777) on the radio altimeter and just retain a little bit (few degrees) the pitch command back with a firm and quite fast move and block the position of the pitch ( do not try to continue the backward movement )
On real airliner that's what we do and then the ground effect will normally play its role and you'll make a very soft landing.

My concern is that this doesn't account for the possibility of running out of runway, and as @RalphJ mentioned, the possibility of a tail strike on longer airframes; but this is good advice if neither of those are factors. Thanks!


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Why is a large flashing "X" placed on a closed runway at Reagan National Airport?
Runway 15 at DCA (Reagan National) is closed at night and other times. By "closed," I mean that airport management places a gigantic lit/flashing "X" in the landing zone of 15. I'd estimate the big "X" is 8 by 8 feet, at least. It's like one of those roadside trailer flashing signs, except it's a runway.
The flashing X is very evident to pedestrians, bikers, etc., on the Mount Vernon trail. It's not some bizarre national secret.
My question: Why, in the tightly controlled airspace of Washington, DC, would DCA need to roll out a giant lit "X" to keep planes from landing there?
As if the obstruction were not there, you could fly in? That doesn't calculate, given how tight the airspace is controlled.
Why does this airport in the center of the world's highest airspace security roll out a construction trailer with a big X to keep planes from landing there?

All the answers were great. I chose the one with the links to external directives, and the photo of the X. I had no idea it was so big.

Well, the answer to "why" is actually "because rules rule". The answer to "why these rules apply to this RWY" is "because they apply to all RWYs"

The standard way of marking a runway as "CLOSED" is to put a big giant X on it - for fields which operate at night that X needs to be lighted. The specifications for the runway closure marker are outlined in an FAA advisory circular (AC 150/5345-55A)
The purpose of the marker is to indicate that the runway is temporarily closed (either administratively, as is the case at DCA, or for construction/repair/maintenance).  It is redundant with air traffic control measures (such as NOTAMs) indicating that the runway is out of service, in case some pilots didn't check NOTAMs or somehow managed to stumble into the airspace and happen upon the airport while it's closed.  (Obviously in the case of DCA they would have other problems were they to wander blindly into the area without talking to anyone, but believe it or not it happens far more often than any of us would like.)

The big flashing X doesn't "stop" you from landing on the runway - it just tells you you really, really shouldn't be landing there. There is a United States Senator who has achieved some notoriety in the aviation community after landing on a closed runway.
The X is also quite a bit bigger than you think it is to ensure it's visible from the air  (the arms are 14 feet long):

(I was looking for a good aerial photo of one at night, but unfortunately couldn't locate one. The intent is for the X to be about the same size as runway numbers so there's no good reason for a pilot to not see it.)

I wonder if that sucker ever blows over from jet blast, or even just the wind? BTW, are these things set up far enough down the runway that someone turning off the taxiway in the wrong place (on to closed runway) would see it? Do they have lights on both sides?

@PhilPerry The runway is closed to departures as well as arrivals, so jet blast shouldn't be an issue (I'd imagine they would get launched though). All the ones I've seen only have one "X" (facing the approach), but I've only ever seen them set up on the numbers (so someone taxiing in at the threshold would certainly see it in front of them). Xs can also be placed on taxiways/intersections to indicate that those are closed to prevent someone from taxiing onto/across a closed runway where necessary (e.g. for resurfacing).

Regarding my question about turning onto a closed runway, I was thinking of the Comair 5191 crash in Kentucky a few years ago. Further reading of news shows the runway in question was apparently not actually closed at the time (was it?), and the crew simply turned wrong in poor visibility. However, my question stands as to whether a plane could enter a closed runway for takeoff, somehow missing the "X" marker, or are all taxiways set up that a plane taking off would have to literally run over the "X"?

@PhilPerry Sometimes the X is just paint (or plastic stuck down on the taxiway/runway, like this one -- Normally a lighted taxiway barricade is also put up in such cases, which you can see behind the X in that photo. In the Comair 1591 case the runway was just "not active", so no X - Runway status lights & colored/switched lead-in lights would mitigate incidents like Comair1591, but they're not commonly installed (yet).

Hmm. With a "flat" X like that, how is visibility while landing? I could see the whole runway being so foreshortened by the shallow angle of approach (and nose-up attitude) that it could be difficult to pick up an "X" like that, especially if you're not in a frame of mind to expect it. How about stretching the "X" vertically (along the length of the runway)? Does that work/is it done?

@PhilPerry Daytime, pretty good (you'll see them on approach or in the pattern). Nighttime, pretty lousy (except when you're taxiing and your lights are shining on it). If you do a Google image search for "Closed runway" you'll find a lot of images with varying quality yellow Xs. Much like with the lighted one the sizes are standardized, and one is placed right on the runway numbers to make it obvious the runway is closed.

Any time that a runway is closed, it is marked as such by an X on the runway so that pilots will know, visually from the air.  At night it is lighted.  This is an additional measure that is used to help protect people and equipment on the ground along with the aircraft if a pilot were to make a mistake and land on the wrong runway.
It is even more important than normal at this particular airport because the runway threshold for runway 19 is very close to that of 15 and they are on similar headings.  The Jeppesen airport diagram even includes a note which says "Be advised some aircrews mistake runway 15 for runway 19" (although the one below doesn't include this note).

This is particularly important at DCA because aircraft landing on runway 19 will either by flying the LDA 19 or River Visual 19 approaches if landing to the south.
Take a look at these approaches:

You'll notice that you approach the airport lined up with runway 15 until very close in when you follow the river and turn for runway 19.  Having flown into this airport a number of times, it is easy to misidentify the runway if you are unfamiliar.  Putting a big X on the runway when it is closed increases the situational awareness and helps identify the proper runway.  You'll note in both procedures you must be flying visually to make the turn and identify runway 19, neither approach lines you up for that runway.  There is no straight-in for runway 19.

If you're in DC sometime, go to Gravelly Point Park for a great view of planes on this approach. https://maps.google.com/maps?q=Gravelly+Point,+Arlington,+VA&hl=en&sll=38.880816,-77.102156&sspn=0.226904,0.528374&oq=gravelly+point&hnear=Gravelly+Point&t=m&z=17)

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Why do some military aircraft use variable-sweep wings?
There are a couple of American military aircraft (the retired F-14 and the B-1 come to mind immediately), that have variable swept wings.  I know that they keep the wings full out (roughly perpendicular to the body) during take off and landing, and they have the wings swept back for high speed flight.
But I've never really understood why? I assume that at lower speeds the wings-out configuration creates more lift.  But, why does sweeping the wings back help at high speed?
For bonus points: how does the performance gain make up for the cost in weight and complexity created by having a variable swept wing?  Or perhaps there isn't much of a gain and that's why most military aircraft don't have variable sweep?

I can't write up a whole answer right now, but basically a wing with higher sweep has less drag at high speeds.  Unfortunately, it doesn't produce enough lift at slower airspeeds so they would have to land extremely fast if it stayed that way.  This design allows them to get the "best of both worlds".

Ah, okay, I can see that on a basic level. I'd love to see your whole answer when you have a chance.  Details are always appreciated :).

Study here. Smithsonian article here

I was hoping for something slightly less technical than the first article (though I'll give it a try) and the second link does not appear to be working.  Still, that does seem to have it well covered...

Another worthwhile link: https://en.wikipedia.org/wiki/Swept_wing

Note that to fly even faster, you would not use any wings at all - that's called a rocket! So the fighter is half way converting to a rocket. It's even relevant in real life: There was an accident where a fighter disintegrated in flight, loosing both of it's wings. The pilot managed to fly and land the rocket he was now flying safely - roughly speaking.

I'm trying to find a reference for that crash - not sure I remember accurately.  If anyone has it at hand, please comment. For now, I found a F-15 landing with one wing - which sounds much worse than no wings at all...: http://www.military.com/video/military-aircraft-operations/crash-landings/f-15-one-wing-miracle-landing/660534011001

By sweeping wing backwards, you essentially make the air 'see' another airfoil.
Look at these two diagrams:

When the air meets the wing, it travels along $V$. This 'seen' airfoil is a lot thinner than $V1$ (which is perpendicular to the leading edge).  As the aircraft experiences less pressure, the aircraft experiences less drag. However, this also reduces the velocity of the air. This is good if you're looking to delay things such as shockwaves as the air goes supersonic, since spreading the force out more delays this effect and the flow separation which comes with it.

Unfortunately, for all the advantages, It would have a very high landing speed. So the wings are swept forward, the aircraft has a more effective aerofoil for lower speeds, and the minimum airspeed decreases correspondingly. There is now more drag, but also more lift which you need for the slower speed.

Wikipedia puts this nicely in not all too-complex terms:

If we were to begin to slide the wing sideways (spanwise), the sideways motion of the wing relative to the air would be added to the previously perpendicular airflow, resulting in an airflow over the wing at an angle to the leading edge. This angle results in airflow traveling a greater distance from leading edge to trailing edge, and thus the air pressure is distributed over a greater distance (and consequently lessened at any particular point on the surface).
This scenario is identical to the airflow experienced by a swept wing as it travels through the air. The airflow over a swept wing encounters the wing at an angle. That angle can be broken down into two vectors, one perpendicular to the wing, and one parallel to the wing. The flow parallel to the wing has no effect on it, and since the perpendicular vector is shorter (meaning slower) than the actual airflow, it consequently exerts less pressure on the wing. In other words, the wing experiences airflow that is slower - and at lower pressures - than the actual speed of the aircraft. One of the factors that must be taken into account when designing a high-speed wing is compressibility, which is the effect that acts upon a wing as it approaches and passes through the speed of sound. The significant negative effects of compressibility made it a prime issue with aeronautical engineers. Sweep theory helps mitigate the effects of compressibility in transonic and supersonic aircraft because of the reduced pressures. This allows the mach number of an aircraft to be higher than that actually experienced by the wing.

Is there a performance gain? Depends on your definition:
Having fixed swept wings would imply that:

The landing speed might be unacceptably high, and with that, long runways would be required.
You could design a fast and light aircraft.Take the F104 Starfighter for example, which had thin, short wings for the same effect but couldn't move them, and was extremely dangerous at slow speeds.

Having variable wings:

The F14 was intended for carrier operations, where you would want a
slow landing speed. Making an aircraft go that fast would probably have been impossible otherwise. It was also designed for long range operations, adding weight of fuel.
Adds weight and mechanical complexity to the airframe, which increases maintenance cost and fuel burn.

If I understand it correctly, today aircraft today rely more on system such as high-lift devices like for instance slats and flaps.

Perfect, great answer @Manfred.

Unsweeping the wings does not actually reduce the stall speed that much, because stall speed depends on wing area and that only changes a little. But it significantly reduces induced drag, because that depends on wing span and that changes significantly.

VG also adds size, as you lose internal space to the wing mechanism, and need larger engines and fuel tanks to get the same performance (all of which means you need more power and fuel again as your weight goes up even more). Hence VG aircraft have tended to be rather large (and AFAIK all except the MiG-23/7 were twin or four engined).

Swing wings combine the high sweep angle helpful for Mach 2+ flight with tolerable low-speed handling characteristics. They were needed to fulfil the demands on military aircraft called for in tenders before planners realized in the late Sixties that high speed was not needed.
When flying at supersonic speed, it helps if the sweep angle of the wing's leading edge is higher than the Mach cone angle. Since the Mach angle goes up with the arcsine of the Mach number, this requires more than 60° of sweep at Mach 2 and 70.5° at Mach 3. If the sweep angle of the leading edge is higher, the flow around it will still be similar to that of subsonic flow around a straight leading edge. This leaves effects like the suction peak near the leading edge in place which would disappear once the flow component perpendicular to the leading edge becomes supersonic. A subsonic leading edge greatly lowers drag at supersonic speed.
Sweep helps also to make the transition into the supersonic realm more gentle by lowering the drag maximum encountered around Mach 1. But below Mach 1 it starts to become a liability. Sweep

reduces maximum lift
requires longer take-off and landing runs
produces undesirable stall characteristics

Therefore, a wing swept by more than 60° becomes rapidly irreconcilable with regular military requirements like short field length and good subsonic handling characteristics at high angle of attack. A swing wing is the only way to combine acceptable high- and low speed performance.
The disadvantages listed above disappear below about 15° to 20° sweep, but the lengthwise travel of the wing's center of pressure with sweep angle is greatest at low sweep angles. In order to keep this lengthwise travel as small as possible, the regular range of sweep angles is mostly between about 20° and 70°.

F-111: 16° - 72.5°, top speed Mach 2.5
F-14: 20° - 68° (in flight), top speed Mach 2.34
MiG-23: 16° - 72°, top speed Mach 2.32
Su-24: 16° - 69°, top speed Mach 1.35
Tu-160: 20° - 65°, top speed Mach 2.05
Panavia Tornado: 25° - 67°, top speed Mach 2.2
B-1A: 15° - 67.5°, top speed Mach 2.22

But there is more to sweeping wings:
The main benefit for the B-1B  and the Tornado (which were both supposed to penetrate air defense at low altitude) is the lower lift slope of a swept wing, in combination with the high wing loading of a swing wing design. This translates into much better riding qualities in turbulent air. If the plane hits an updraft at high speed and in the high density air near the ground, the lift increase is massive if the wing is unswept. Sweeping it reduces the lift increase with the cosine of the sweep angle, and a gust which would have produced 4 g with the unswept wing produces only 2 g with 60° sweep. This effect is further increased by the change in wing span, which will reduce the load factor even more.
The other benefit is the possibility to use high-lift devices on the wing. The trailing edge comes forward and out for the landing configuration, so the pitching moment of the flaps can be controlled by the elevator and more air can be used for lift generation. Trailing edge flaps on a delta wing (which is basically the swept-back configuration), on the other hand, do not work well at all. This is helpful both for landing on a carrier and for taking off for a long-range bombing mission.

So, what kinds of missions are swept wings really useful for then?  You make it sound like there's not really enough of an advantage to justify ever really using them?

@Jay Carr: Did you want to say "swing wings"? Wing sweep is immensely helpful in order to fly close to Mach 1, above Mach 1 with a subsonic leading edge, for low gust sensitivity and for reaching high angles of attack in a controlled way. Swing wings, on the other side, are helpful only in a few special cases and in most applications did not fulfill the initial targets of the designers.

lol, yes, I meant swing wings, sorry.  So there's no real practical application?  At least not one that can't be done a bit easier by other means?

@Jay Carr: I hate generalizations, so I will not use one here. But in most cases, thinking a little harder how to make things more simple pays off. A swing wing will immediately solve a lot of problems, but will introduce different ones, first of all more mass, more demands on systems and more internal structure. Making the aircraft smaller and simpler might save the need for the high-lift forward wing sweep configuration.

Swing Wings were useful, and are still useful. Its just that the increasingly higher speeds are not needed by aircraft anymore. Back in early 1960s, the main nuclear weapons delivery platform was bombers. Which needed to be intercepted, and that required speed. Bomber speeds also kept increasing, so that required even higher speed for interceptors. Intercepting or not intercepting was the difference in 'winning' a nuclear war. Hence the swing wings for fuel efficiency for low speeds (cruise) and shorter take off/landing AND high supersonic speed..... But with the ICBMs, that need was no more.

Therefore, the aircraft starting with late 60s and on, lost the swing wings. Their use has become more tactical than strategic. There can be no 'strategy' to be played out in a war in between nuclear powers with icbms.

Well the problem is not only the lift created but also the drag. At high speed transonic and hypersonic, the drag created by straight wings is much larger than the drag created by swept wings (or even better by delta wings). This mainly comes from the fact that due to the sweep angle the effective Mach number the one perpendicular to the leading edge of the wing is lower than the Mach number of the aircraft. This helps a lot in reducing the drag due to chocks and thus sustain very high speed with not too much drag and hence thrust required. So far so good, but...
Delta wings and at smaller degree swept wings at low speed present what is called a spanwise flow. This is the fact the the flow is pushed in the spanwise direction from the root to the tip. This increases the distance of the flow over the wing and thus the boundary layer thickness at the trailing edge (compared to straight wings). This has the immediate effect to lower the stall angle or at least the angle at which the first separation appears. This also reduces the lift generated when the aircraft is flying at a non negligible angle of attack. This is particularly the case for take of and landing for which the straight wings yield better performances.
To sustain the aircraft in the air with a smaller angle of attack means to fly faster and this is obviously not is looked for during take off and landing. This is why it is beneficial to use variable swept wings for some military aircraft which need to take off or land on short distances and then needs a smaller take off and landing speed.

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All approaches at airport NA for Alternate planning. Does that mean the same as Airport NA for Alternate if VFR landing is planned?
Jeppesen will use the term "NA" in the "For Filing as Alternate" table if all the available approaches at the given airport are not available. For FAA charts, a pilot will know that an airport is NA for alternative planning purposes by looking at all procedures and noting the boxed "A" NA for all approaches.
I've been under the impression that NA is, well NA. This airport is not usable for planning purposes. Which bring me to an interesting question. What if the weather supported a descent from the MIA/MVA to landing under VFR? In other words, no IAP is planned.
VFR only airports are approved as IFR alternate airports assuming the weather supports a descent from MIA/MVA to landing under VFR. Assuming we had great weather in the vicinity of our required IFR alternate, why is it okay that a VFR only airport is approved but the IFR airport is NA?
I understand the reasons why there is an "NA" such has unmonitored NavAid and lack of reporting WX, etc. But that would all assume we were planning on an IAP at the alternate. If that is not the plan, in otherwise, a VFR landing from the MIA/MVA, then I don't see a reason why the airport could not be listed as an IFR alternate?
Lastly, along the same lines. Non-WAAS equipped operators may file a destination and alternate airports based upon a GPS approaches, just not both. The scenario is this. The destination has only a RNAV(GPS). The desired alternate has the same as well. Again, I would agree that the desired alternate is unavailable to this pilot due to lack of conventional navigation approaches (planning purposes only). But once again, if this plan was a VFR landing from the MIA/MVA, (The GPS approaches is not planned on) and the weather forecast supported this, then again I don't see a reason why this airport couldn't be filed as an IFR alternate?

I'm not a pilot and I may not be understanding your question fully, but I have heard that one reason all approaches could be "NA for alternate planning" is if the airport does not have full-time WX reporting capability. If the weather happens to be VMC at the time of your diversion you could go there, but you can't plan on it because if there's no ASOS or certified observer then there's no way to find out besides actually flying there yourself.

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Selection of cruise FL and semi-circular rule
Let's assume I am flying VFR from A to B.
B is located north-northwest of A, eg. a direct course would yield a magnetic track of, say, 350°(M). However, some legs of my route are northeastwards, before dog-legging northwestwards, eg. 020°(M) then 340°(M).
In that case, how do I apply the semi-circular rule when selecting a flight level? Would I:

only consider the location of my destination relatively to my departure, and my route as a whole, and select an even FL+5?
select my flight level leg-wise, ie. flying at an odd FL+5 in the northeastwards part of the route, then even FL+5 when adjusting westwards?

The selection of a level is based on your aircraft track, so you should always adjust based on the current leg not the overall track of origin to destination.
(Highlighting in the following is mine.)

The VFR rules of flight level and/or altitude selection is the same as IFR ones with adding 500ft to all levels.
The default worldwide semi-circular rule is the East/West orientation of the flight level parity:

Your aircraft has track between 0° and 179°, your flight level or altitude must be odd.
Your aircraft has track between 180° and 359°, your flight level or altitude must be even

source: https://wiki.ivao.aero/en/home/training/documentation/Semicircular_rules

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How to solve normal and axial aerodynamic force coefficients integral equation to calculate lift coefficient for an airfoil?
$$ c_n = \frac{1}{c} \left[ \int_0^c (C_{p,l} - C_{p,u}) \, dx + \int_0^c \left(c_{f, u} \frac{dy_u}{dx} + c_{f,l} \frac{dy_l}{dx} \right) dx \right] $$
$$ c_a = \frac{1}{c} \left[ \int_0^c \left(C_{p, u} \frac{dy_u}{dx} - C_{p,l} \frac{dy_l}{dx} \right) dx + \int_0^c (c_{f,u} + c_{f,l}) \, dx \right] $$
I am trying to calculate Cl vs alpha curve for NACA2412 airfoil. I have calculated the non-viscous Cp (pressure coefficient) using panel method and Cf (friction coefficient) using Thwaites, Michael's and Head's boundary layer integral equations. I now have both Cp and Cf for all the panels. In order to calculate Cl (lift coefficient), I need to calculate these force coefficients first. I am stuck here, I am having difficulties solving these two equations. Please somebody help me to solve these two integral equations so that I can insert my Cp and Cf values to get Cn (normal force coefficient) and Ca (axial force coefficient). The author left these equations for the readers as an exercise but seems like I am having huge confusions solving it. I can have dy/dx data from the panel method (it is just the tan(phi) for each panel).
Equation source - Fundamentals of Aerodynamics 6th edition(page number - 26)

We also have a [mathematics.se] site.

This is an excellent question! Many people are looking for a conceptual understanding of exactly this problem, and understanding the insights of others, both in the question, and given answer, are helpful.

Image source
In order to find the resulting $C_P$ value over the length of the chord, we need to determine the enclosed area of the pressure distribution plot. Which is what solving an integral equation does.
The equation can be solved analytically if the resulting plots can be captured in a mathematical function of chord length, which would not be my preferred way of proceeding. Or more practically, the values found with the panel method can be linearly interpolated, which is a numerical way of solving.

Each blue rectangle is:

In vertical direction, the average of the two upper points minus the average of the two lower points.
In horizontal direction = 0.1 * chord $c$

Add all 10 rectangles to get the total area; divide by $c$ to obtain dimensionless unity.
Mutatis mutandis for the remaining bits of the equations.


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How did pilots pee on Rutan Voyager?
Rutan Voyager had a very long flight.
Did pilots have a separate toilet room for when they needed to relieve themselves?
How much room did they have to move around anyways?
Is there any visual with the interior of aircraft?

Welcome to aviation.SE! We have a couple of related questions, they aren't specific to the Voyager but they have some general information: here, here.

Glider pilots on very long flights use pee bags made for the purpose with the gel that turns the liquid urine into a solid goo.  Some also use Depends diapers, which avoids certain "handling" issues. https://www.sosaglidingclub.com/uploads/1/6/5/2/16520160/urination_management_module.pdf

Did pilots have a separate toilet room for when they needed to relieve themselves?

Given the size and weight of the aircraft, this would be near impossible. There wouldn't even have been margins in the weight budget for toilet paper, let alone a toilet room.
I don't know if there is any official documentation about their bodily fluids.
I did find this quote:

Rutan even brought a small plastic bag with an adhesive, circular opening to answer the question he said he is often asked first—how did you go to the bathroom?

So, the answer seems to be that they glued a plastic bag to their bottoms.

How much room did they have to move around anyways?

Practically none. The aircraft had room for exactly one thing: fuel. If there had been room to move around, that means there was room that wasn't being used for fuel, so they would either have designed away the room or filled it with fuel.
The pilot flying was lying in a lightweight pilot seat, the pilot monitoring sat or lay on the floor next to the pilot flying.

Is there any visual with the interior of aircraft?

Yes, there are quite a number of photos, which you can easily find using your favorite search engine, for example:

Dick Rutan and Jeana Yeager in Cockpit of Voyager
Rutan Voyager Cockpit
Jeana Yeager

Must be a very big bag for such a long time. Didn't they flush and throw the waste from time to time? Saves mass - and therefore fuel. How much waste they produced in total?

I think the rules for the endurance record(s) they were attempting prohibited "jettisoning" -- but it's not hard to arrange to minimize solid effluent via a few days of low-residue diet.  Takes a few more days after the attempt to resume normal intestinal operation...


text:
What is the reason why dihedrals are used when building a plane?
How does dihedral affect flight characteristics of a plane? I know it increases stability, however is it the only reason why it is implemented? If so, aren’t there more effective methods to stabilize the plane?

Welcome to aviation.SE! We have a number of questions about dihedral already that might answer some or all of yours, e.g. here, here, here. Do any of those help?

Does this answer your question? What kind of dihedral would be most stable?

As explained in the help center, you should indicate the current state of your research.

Because when an airplane rolls to a bank angle, the airplane begins to slip toward the lowered wing.  If the wings are mounted with a dihedral, this causes two things:  the inside wing will experience an increased angle of attack, and the outside wing experiences a decrease in angle of attack.  This combination causes an imbalance in the lift forces on the wings resulting in a rolling moment about the center of mass and returning the airplane to a wings level condition.
Dihedral angle is much more common on low wing airplanes, since the location of the CG above the CL creates a static unstable roll condition when the airplane is banked.  Dihedral angle can be used on high wing aircraft as well to enhance roll stability along with the pendulum effect of the CG below the CL e.g. a Cessna 172 still employs a slight dihedral angle to its wings.
In the age of digital flight control systems dihedral angles to wings are not absolutely necessary, though for light airplanes and gliders it’s far more elegant to design the airplane with a slight natural static and dynamic stability in all three axes.  Aircraft designers also work to ensure that airplanes have more authoritative directional stability than lateral stability from a dihedral angle to prevent unwanted Dutch rolling tendencies.

"Having CG above CL creates a static unstable roll condition", I'll save our PK a few years of journalism, it's having CG "above" center of lateral drag (as plane slips sideways) creates a static unstable roll condition.  Putting the wing high actually raises the CG, allowing for more side area underneath it.  The designer then rebalances with an upward vertical stabilizer, the "classic" high winger.  The designer can add a touch of dihedral as needed, as it improves roll stability, as well as "self righting tendency" recovering to straight and level from a bank.  Shame they closed this.

First let's define dihedral.
It's when there is an angle between the wing root and the wing tip. Usually a positive angle.
Dihedrals wing are desinged to increase the lateral stability of the airplane. For example, if there is a wind gust (updraft on the right wing) that makes the airplane roll to the left, the result will be a lowered left wing and a raised right wing.
With the dihedral, the lowered wing (left one) has a greater AOA than the raised wing, therefore producing more lift and bringing the dropped wing back to it's original position.


text:
How can I find a deregistered airplane?
I'm trying to find a 1959 C172 tail number N7393T.
It was my grandfather's and the last registered record of it was near Glendale AZ.  It was deregistered in 2015 and I found out that since it cannot be reregistered for 5 years it may have a new tail number. Any tips on tracking and finding this plane would be helpful.

A quick search on my favorite search engine orient me to flight aware. Then I tried to put the serial number on the FAA registry but without luck. I cannot find any references to this serial number after 2015. What other methods did you tried before asking your question?

Here’s a helpful link : https://aviation.stackexchange.com/q/102715/70478

Sorry to be the bearer of bad news. But, you have already asked this question on www.airport-data.com. A quick search in the FAA search database with the tail number or serial number (which can be found using the tail number) shows that it has not legally flown in the US in almost a decade. So, it is either sitting somewhere as a ramp queen, registered overseas, or not in existence any longer.
Try contacting the last person to register it. Otherwise, it would be like trying to find a salvaged car after it has been junked. It will only pop up if it is reregistered. However, you can pay a private firm like a law firm to research the aircraft’s certificate of title (or simply title). It would be like searching a deed.

Thanks>  yeah I was trying a couple different forums to expand my search but thanks for the help.  I've tracked it so far to Glendale AZ.  I'll hopefully find it

@MichaelMatt - I wish you the best of luck in finally finding it. Post an answer with a picture of it when you do. Maybe a description of how you were able to locate it, too.

You could try a search at Landings.com.
They have a serial number search link.
http://www.landings.com/evird.acgi$pass*193800885!_h-www.landings.com/_landings/pages/search.html


text:
How is an A320 on the ground kept cool inside if the APU fails?
What happens to the air conditioner when the APU is not available due to damage or it just fails?
Also adding that the airport does not have an air conditioning unit. Since it is above average sea level, what procedures should be performed?

Depending on turn around, they may just keep one engine running, especially not having bleed air for a restart.

Can one or more packs run with ground source?

They can leave one engine running to take the place of the APU. If that's not possible for whatever reason, the interior just gets warm.

And they cannot start the engines again without an external huffer, which probably means they might try and swap the plane in case they can't leave the engine running.


text:
What procedures do I have to follow to fly a seaplane from the US to Canada?
I work in the States and I'm thinking to go visit my friend in Canada. I have access to an Icon A5 and was thinking to fly from my closest lake in Vermont to his house which is also on a lake. What would be the protocols for doing this? Customs wise. Since I believe I would have to file a flight plan. How would immigration work since I am not planning to land at an airport and I'm also not a citizen of either the US or Canada?

Welcome to aviation.SE! This question has a lot of relevant information, and this one might be helpful too. AOPA has an entire guide on flying to Canada. Your final question about immigration rules for non-citizens would fit better on travel.SE. And note that right now the US-Canada border is closed.

You might get some good tips here, but make sure you research from original sources like:  https://www.cbsa-asfc.gc.ca/prog/canpass/privateair-eng.html.  Ditto on what Dean said about the port of entry.  That is the key takeaway.  You can't just land anywhere.  Call ahead, file a flight plan, etc.

Separately from the aviation aspect, have you addressed Canada's COVID travel restrictions (see also this page)? Visiting for tourism is not permitted, and even if you meet one of the exceptions to be allowed in, there's a 14 day mandatory quarantine requirement.

Whenever you land in the US from a departure point not in the US, you have to land at an Airport of Entry as your first US destination airport. It does not have to be a big airport. There are plenty of Class D airports that qualify. You can verify which airports are AOEs in the US Chart Supplement. Some (big ones) are also marked as such on the sectionals.
When crossing the US border, you will need to have arranged customs clearance with the US CBP beforehand if you are landing at a small AOE. You may also need a US CBP DTOPS decal for your aircraft. Then, of course, there is the flight plan. Once you have cleared US CBP, you can fly to any other US domestic destination of your choice.
I would think that when flying into Canada, the TCCA would have similar rules.

You know, while great info, this really doesn't answer the question.  Can one cross the CAN border with a floatplane??!

@Fattie, yes, if a port of entry exists on a seaplane base.  Up here in the PNW Beavers go back and forth regularly.  There is a US Customs office right next to the dock at the lake a few miles from my house.

@Fattie:  Sure it does.  It's just that it only answers the question for southbound crossings.

It works the same going the other way too.

@Fattie - To be clear, you can fly a floatplane from the US to Canada. Whether you can fly a seaplane from the US to Canada, and land it on a Canadian lake as your first destination point is another story. That would depend on the status of the lake upon which you land. Is it a port of entry? And, has customs been arranged beforehand? It can’t just be a random body of water.


text:
Why do certain aircraft's landing gear tilt up?
Why do the main landing gears of aircraft like the A330, 777, 787, etc tilt up? This does not happen with the 767. Interestingly, for the 747, the inner landing gear does not tilt up while the outer landing gear (under the wing) does. Why does that happen?

To clarify, the main gear of the A330, 777 and 787 appears to be configured so that the trailing wheels of the bogie are lower than the leading wheels before landing, whereas the 767 seems to be configured to have the leading wheels lower. The plane whose gear is pictured is moving from left to right.

Yes, I wanted to understand why that is so (the landing gear being tilted).

I just found a youtube video explaining it.

Pulling mostly from the answers provided here it seems that

The torque produced by the straightening gear helps to flatten the plane out.
The main gear tilt on the B747 also provides air/ground sensing. All four main gear bogeys tilt when the aircraft is airborne, so on touchdown any systems relying on air/ground logic can activate
The gear is tilted to fit into the wheel well

You can check the link for the rest of the explanations.

On that thread, it is also explained why the 767 is different:
Interesting note, the 767 has the unusual tendancy to pitch down quite rapidly during landing, which is why the MLG on the 67 is tilted forwards. Upon touchdown, the MLG straightens and stops the pitching forward. The downside to this, however, is that the the forward gear on the MLG touchdown first, so the 767 landing is quite a bit rougher than the 757 or the 777, both of which have up-tilted gear

The gear is tilted to fit into the wheel well uhm, is that person sure not to be switching cause and effect?

@Federico, apparently not; see the other answer. The thing is that the gear needs to be in a specific position for retraction. And while it could be designed for any position, the maximum tilt (either forward or backward) is easier to achieve as the actuator only needs to act in one direction.

"The main gear tilt on the B747 also provides air/ground sensing. All four main gear bogeys tilt when the aircraft is airborne, so on touchdown any systems relying on air/ground logic can activate"  Uh, no, only the wing gear tilt when airborne; the body gear remain level (pic).

I will use the 757 as an example, but everything is true for every multi-axle landing gear I've ever been around (except the 777).
The truck (bogie) is tilted into a specific angle so that it'll fit into the wheel well, all other functions are secondary. The truck must be angled because the landing gear strut itself is not completely perpendicular to the fuselage, due to other considerations. This is what the 757 Maintenance Manual says about the truck position actuator (aka tilt actuator): "This actuator applies the force to put the truck assembly at an angle to permit clearance with the structure."
This YouTube video shows the extension/retraction of the 757 landing gear, you can clearly see in the video that if the truck was not at a specific angle it would impact either the keel beam or the wing to body fairings.
The reason it stays tilted in the down position comes down to cost and complexity. The actuator is a simple one-way hydraulic actuator, meaning it can only be powered into the extended direction. Any time hydraulic power is supplied to the landing gear, either in the up or down position the truck positioning actuator is powered on the extended side, regardless of gear position.
Extra information, for the non-TL:DR crowd
When the aircraft touches down, the actuator attempts to keep the truck tilted, which massively increases the pressure in the actuator (normal system pressure is 3000psi). A check valve prevents the hydraulic fluid from being forced back into the hydraulic supply system, then at 4500 psi dumps the fluid into the return allowing the actuator to collapse. At takeoff when the aircraft rotates it again forces this actuator even further into the retracted position as the aft wheels get closer to the fuselage. As you can see the stroke of this actuator must be quite long. So fully extended gives you a toe up position and fully retracted gives you a toe down position.
To have the truck powered to any position other than fully extended would first require the ability to power in both directions, which adds a lot of complexity to the hydraulics system and actuator and this would only get you fully extended and fully retracted. To position the truck in any other position would require complex control valves with position feedback or multi-position actuators and also sequence valves to ensure any time the gear was not down and locked the truck was in the proper position. Since there is no need to flatten the truck for landing, this is not down.
Finally having the truck position always powered fully extended means the truck will always be in the correct position for retraction and you can use the truck tilt to detect air/ground (weight on wheels). In fact on the 757, if pressure to the truck positioning actuator fails, the aircraft will not switch to ground mode until the nose gear shows weight on wheels.
To address the nose down moment that has been mentioned, while technically this does happen the moment is very small relative to the aircraft and is over in a fraction of a second. The actuator itself is fairly small, smaller than a spoiler actuator and reacts its load on the strut very near the truck pivot pin, so the moment arm is short. Also this same force would fight against aircraft rotation at takeoff.
The 767 does nose down because its struts are at a different angle than the 757 and they have to be nose down to fit in the wheel well, this is a design decision due to a limitation at LGA.

"The truck (boogie) is tilted..."  Pretty sure it's a bogie, not a boogie.

I'm not convinced the video really helps to explain this. To my eye, the 757 gear looks like it extends with the bogie pretty much parallel to the ground.

@DavidRicherby I guess it helps that I know what it is supposed to look like. But if you look at the 55 second mark, the camera is fairly straight on and you can see the front tire is higher than the aft tire. Then you can watch the retraction and extension and see the truck never pivots. At 4:26 he also shows a side video of the LH gear and you can see the forward tire is higher than the aft, then at 4:56 you can see that if the truck was at any other angle it would hit the structure.

@OSUZorba OK, with explanation, that makes more sense. At 55s, I supposed I was just seeing a level bogie in perspective but I guess the camera would have to be 10ft in the air to see that. Actually, it might help to set the video start time to about 4:20, since the side view at the end of the video seems to make the angles much clearer -- at least, to me.

@DavidRicherby It doesn't appear that the start times in the link are actually working, at least not for me in Chrome or Firefox.

@OSUZorba Sorry -- I messed up (long story short: if you copy-paste from YouTube's "share" link, it's at youtu.be; if you copy-paste from your browser, it's from youtube.com. The two use a different URL format and I didn't notice). Now fixed. I set it to start at 4:20 but, of course, you should change that if you think there's a better time.

I really would LOVE to know details about such limitation at LGA, could you expand it, @David Richerby ?

@user18674 It's OSUZorba who made the claim about LGA, not me. My edit just changed the start time of the linked YouTube video.

True, thanks! @OSUZorba, do you have more details about the limitation in LGA?

@user18674 I don't know of a public source that is definitive, be here is a link with some more information: http://www.airliners.net/forum/viewtopic.php?t=766253#p11060455

On A340 at least, where the -600 variant is very long , this takes advantage of bogie to maintain a high AoA at touchdown, while not having longer struts.
The design is then kept for the whole A330/A340 family.


text:
Are there any drawbacks to requesting progressive taxi every time?
Unless you know the airport like your own backyard, it seems like requesting progressive taxi would always be the safest option to essentially eliminate the possibility of taking a wrong turn or busting a hold short. Aside from the risk of slightly annoying the folks in the tower, are there any drawbacks to requesting progressive taxi as standard operating procedure?

What size of airport do you have in mind? I guess for a major international airport at rush hour it will be more than "slightly annoying the folks in the tower" if every single aircraft requests progressive taxi...

There's a Japanese line of ATC sims imported into the U.S. as the "Airport Hero" series. They strike a good balance between realism and game. The game puts you in full control of how each aircraft taxis, and micromanaging taxi routes is one of the most challenging aspects of the game. I've often found myself yelling at the virtual pilots for being so dependent on me.

Land at many airports in Europe and the only taxi instructions you will get are: "Follow the follow-me car." Even if you know the field like the back of your hand. That might be safer than progressive taxi.

I'll be shocked if there isn't someone working on a fully automated solution for this right now.

@kojiro There is. See for instance http://followthegreens.com/

Apart from appearing really unprofessional, the obvious drawback is a significantly higher workload, both for the pilot but especially for ATC. You're not the only aircraft moving around at the airport, and even if you are, the controller most likely has other things to do than focus entirely on you.
As a pilot, you will also have a lower situational awareness, since you are not actually keeping track of where you are, but just following turn-by-turn instructions. Are you 100% sure you are at the right runway? And that the runway is long enough? What was the departure procedure again? Is the aircraft correctly configured for takeoff? I guess you didn't have time to check the charts, do a departure briefing and run through checklists since you had to focus on the radio all the time.
A more subtle drawback is that the controller will trust you less and as a result may very well choose to delay you in some situations. This is not written in any books, but controllers do establish sort of a mental picture of a pilot's competence level while talking to them, and if someone repeatedly requested progressive taxi, that would certainly raise a red flag. If you're waiting in line for takeoff, and there is a gap between arriving aircraft just large enough to get you going, the controller is more likely to let you wait for a better opportunity if they do not trust you fully. What's to say an (apparently) inexperienced pilot won't line up and spend 30 seconds on the runway before applying power - forcing a go-around for the aircraft on short final? Best wait another few minutes until there is a larger gap.
Ultimately, if you are in doubt about where you are, PLEASE DO ASK the controller for help! But, if you plan on making a habit of it just for convenience, please know that you are abusing the system, potentially reducing ATC capacity and causing an unsafe situation for yourself or others.


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What are the margins used to avoid a stall while slipping near the ground?
Similar questions have been asked before, but in life-and-death questions like this, I want to be certain. This question is about airplane behavior close to the ground in normal and/or near slow flight.
I know that based on the angle of attack, a stall can occur at any airspeed. Alas, what should/does the IAS measure?  Presumably, it is from a pitot tube extending from the wing, straight into the relevant wind that is to fly over the wing, so if the angle of attack becomes very high, presumably the IAS dives, too.
For a small 2-seater or 4-seater with a modern wing (like a Diamond or Cirrus or Flight Design), is an indicated airspeed of 10 knots above stall speed a sufficient guarantor for not stalling?
For example, in a slip near the ground, if my configured stall speed is 60, and I fly it so that my IAS steadily drops down to 70 in my uncoordinated slip (at which point I relax back pressure to keep IAS at 70), am I then assured that the airplane cannot enter a stall?

You should read How it flies?. It provides insight about flight dynamics and speak about IAS.

I changed the title to be more  specific and to be a question. Fell free to re edit it if it does not fit with what you meant (in which case you may consider editing your question to be more clear)

it's a good title that describes what I ultimately want to know.

When I side slip my glider "correctly" the airspeed indicator drops to zero or at least shows large fluctuations between 30 to 90% of the actual airspeed. So the airspeed indicator essentially becomes worthless during a large side slip and can't give any estimate whether the aircraft is approaching a stall or not. And I wouldn't rely on it to judge if the aircraft is approaching a stall.
I can somewhat judge the speed from the sound of the wind and also how much rudder input creates what kind of side slip (slow usually creates more slip angle for full rudder deflection) and also the back pressure needed but the best indicator for the approaching stall is still the elevator buffeting or an angle of attack indicator or angle of attack warning. If you're planning on doing short field landings with low approach speeds then an angle of attack indicator is probably a good investment.
From a physical standpoint the indicated airspeed in a side slip condition should always be less than or equal to the airspeed that you're actually flying. So if you see an airspeed indication in a side slip configuration you're going to have at least that figure as actual airspeed. This is because the airspeed indicator just shows the difference between atmospheric pressure and total pressure (sum of dynamic and atmospheric pressure). And if you rotate your pitot tube from 0 degrees to 90 degrees off the direction of incoming air it will show less and less dynamic pressure and work more like the static port, thus the readout drops. But it can never show more than what the dynamic pressure actually is (disregarding small vibrations due to unstable inflow). So if you look at the airspeed indicator and judge by the speed it reads you should be on the safe side.
Whether or not the 10kt increment is enough depends on how steep your side slip is and what you are flying. Ground effect could also influence how much angle of attack is left before the stall. Only a numerical simulation would give you an exact number here.
But you can always experiment high up in the air, do a side slip down to what feels as low as you would want to go for a safe landing and then pull up even more and see how far you can go without it stalling or see how it departs (relax controls immediately to avoid any nasty spins) if it actually does anything. Maybe it will show some significant buffeting before it actually stalls (great indicator!), maybe it will just lower the nose (not ideal close to the ground but still safe) or maybe it drops a wing (not so good, add more safety margin).

I think the short answer in here is that IAS is not a good indicator of AoA.  (I read up...it requires a second pitot hole to get an AoA.)  Thus, in the absence of an AoA in the airplane, the only warning may well be the stall buffeting for a well-designed aircraft, and near-nada for a more dangerous one.  true?  if so, please add for marking this question as answered.


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How does the FAA BasicMed affect the safety pilot for somebody flying under the hood?
When one pilot is practicing instrument flying with a view limiting device (a "hood"), a licensed pilot needs to be along to watch for traffic (the safety pilot). There are several scenarios where none, either, or both are instrument rated, and the flight could be held in IMC or VMC. In this case neither pilot is instrument rated and are just following VORs in visual flight rules.
BasicMed applies to certain aircraft, so lets assume we are talking about your ordinary general aviation IFR capable aircraft with 4 seats and 150 knot cruise speed, while flying VFR.
The FAA states this in their FAQs:

Q25:  Can I use BasicMed to act as a safety pilot, rather than holding
  a medical?
  A: Only if you’re acting as PIC while performing the
  duties of safety pilot.  The statutory language prescribing BasicMed
  said it only applies to people acting as PIC. BasicMed cannot be
  exercised by safety pilots who are not acting as PIC but are required
  crewmembers.

I find this confusing, aren't safety pilots acting as PIC because they are required crewmembers?
This question suggests that a BasicMed pilot can only be a safety pilot in VMC:Logging PIC time during IFR flight in VMC.
So my question is this (because it pertains to my present situation): Can I be a safety pilot for a non-instrument rated pilot when I have my BasicMed physical, as long as the flight is in VMC? Can I log PIC time while the pilot under the hood is flying? I should, because I am the PIC as safety pilot.
It would be nice if the FAA gave more clarification, and examples for all the practical scenarios pilots would experience. The safety pilot issue itself confuses a lot of people, now we have BasicMed regulations to add to the confusion.

Short answer: the safety pilot with BasicMed must be acting as PIC, but all other regulations and considerations are the same (i.e. as if the safety pilot had a regular medical).

You have quite a lot of points in your question, but I'll try to break it down.
"[...] aren't safety pilots acting as PIC because they are required crewmembers?"
Not always. Being a required crewmember is not necessarily the same as being PIC, e.g. a typical airliner requires two pilots but only one of them is PIC. When you fly with a safety pilot there are two ways to do it:

The safety pilot acts as PIC; the pilot under the hood is a required crewmember
The pilot under the hood acts as PIC; the safety pilot is a required crewmember

As you (and the FAA FAQ) said, BasicMed only allows pilots to act as PIC, not as non-PIC required crewmembers. Therefore only scenario 1 is possible for a safety pilot with BasicMed.
Practically speaking, scenario 1 is what most people do anyway, because it allows both pilots to log PIC time; remember that acting as PIC and logging PIC time are two different things. (In scenario 2 the pilot under the hood would log PIC time but the safety pilot would log SIC time.)
"a BasicMed pilot can only be a safety pilot in VMC"
The concept of a safety pilot only applies to VMC; in IMC you're in real instrument conditions, not simulated ones. Perhaps you meant VFR, not VMC? This question (which you already found) is about acting as a safety pilot under IFR.
"Can I be a safety pilot for a non-instrument rated pilot when I have my BasicMed physical, as long as the flight is in VMC?"
Yes, if you act as PIC, as described above. And again, a safety pilot is only needed in VMC.
"Can I log PIC time while the pilot under the hood is flying?"
Yes, and this has nothing to do with BasicMed. Because simulated instrument flight requires a safety pilot (91.109), that means that if you're the safety pilot and acting as PIC, then you can log PIC time as described in 61.51(e)(iii) (emphasis mine):

When the pilot acts [...] as pilot in command of an aircraft for which more than one pilot is
  required under the type certification of the aircraft or the
  regulations under which the flight is conducted


text:
At what distance from magnetic north do pilots start referencing true north for heading?
The Earth's magnetic poles are constantly shifting, resulting in a significant distance between the true and magnetic poles. This means that while using them as references for heading at lower latitudes makes sense, using them as such while flying in polar regions causes often unacceptable inaccuracy.
In a simulator, I noticed that many modern airliners have a toggle to switch between referencing true and magnetic north as appropriate; but at what distance from a pole would this toggle be activated?

Whilst the north magnetic pole does shift it is a slow process, and not the reason for using true north at the poles. The reason is that close to the poles the compass will try to point at the ground instead of moving freely.

I hadn't considered that. Good point!

In Boeing aircraft the default is to select MAG. When the aircraft enters the polar region it will auto switch to TRU. The pilot can also select TRU when outside the polar region.
The polar region is defined as north of 82 deg N latitude or south of 82 deg S latitude. It also includes the region north of 70 deg N between 80 deg W longitude and 130 deg W longitude and the region south of 60 deg S between 120 deg E and 160 deg E longitude.

What is the reason for the additional areas below the 82°?

@Czechnology   Those are the areas around the magnetic poles.  Near them magnetic compasses (and heading) are pretty much useless.

@Gerry: So why is most of the true-heading area referenced to the geographic poles rather than the magnetic poles?

@Vikki Because True Heading is defined to be referenced to the geographic poles. The Mag poles drift and the magnetic variation in the area doesn't follow a consistent pattern so it would be difficult maintain up-to-date magnetic variation charts. Most navigators do their underlying computations in true and then apply mag var along the computed route. True heading is directly tied to the Lat/Lon coordinates so it makes sense to use it. Converting it to Mag heading makes it easy to fly with the use of a mag compass. Near the poles, the extreme mag var makes the compass is pretty much useless.

@Gerry: It's difficult to maintain up-to-date magnetic-variation charts, but people do so anyways, since these charts are essential for navigating with a magnetic compass.  And, since the rationale for the true-heading zones existing is the extreme magnetic variation and high magnetic inclination at high magnetic latitudes, it would make more sense for these zones to be centered on (the current locations of) the magnetic poles, rather than being mostly centered on the geographic poles with relatively-small cutouts for the magnetic poles.

@Vikki It's just not about having the mag var charts. Aside from the issues with the compass due to the vertical component near the poles, the fact that the mag var changes dramatically over relatively short distances makes the use of a compass impossible. At typically cruising speeds, the mag var would drive constantly changing headings. Take a look at the map here from NOAA. Zoom in on the polar map. Lay a course line and try to compute a heading.

@Gerry: Mmm, makes sense when you explain it that way.  Also, from that link: "Due to unplanned variations in the Arctic region, scientists have released a new model to more accurately represent the change of the magnetic field" - are there planned variations in the earth's magnetic field?

@Vikki The mag pole has (was) been shifting at a pretty steady rate so they have planned updates to the model every few years based on an acceptable error. Recent shift have been greater than expected so they did an update before the next planned update, hence an unplanned update.


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How does the FAA define fuel capacity for ultralights?
Ultralights under FAR 103 are regulated to a capacity of 5 gallons. I'm wondering how exactly fuel capacity is defined, does it include fuel in the lines, and in the carburetor bowl or elsewhere or just the tank feeding the engine?

FAA Advisory Circular AC 103-7, Paragraph 19 has this to say:

MAXIMUM FUEL CAPACITY OF A POWERED ULTRALIGHT VEHICLE.
The maximum fuel capacity for a powered ultralight vehicle is 5 U.S.
  gallons. Any
  powered  ultralight with fuel tank(s) exceeding this capacity is
  ineligible for operation as an ultralight vehicle.
a. Determination of Fuel Capacity.
The total volume, including all  available space for
  usable and unusable fuel in the fuel tank or tanks on the  vehicle is
  the mtal fuel capacity. The fuel in the lines, pump, strainer, and
  carburetor is not considered in a calculation of total volume.

Okay, so you use exhaust piping for your fuel lines, and get another gallon or two of capacity.

@Mark I suspect if you pushed that and got called on it, you'd find the FAA (or your competition director; powered hang/paraglider comps do "maximum distance on a single tank" tasks) will simply consider that a second cylindrical tank!

@Mark - I know of someone who uses really large diameter fuel lines in his track car, just to get a few extra laps w/o refueling.  Has passed several tech inspections, but I know that isn't the FAA.


text:
Pitching moment as a pure moment and its measurement with a homemade force balance
In mechanics, we learn that a force $F$ acting at a certain application point $P$ can exert a torque (also called moment of the force) about another arbitrary point $Q$ in the plane, i.e. $\tau= F \times PQ$ where $PQ$ is a distance vector.
It is possible to move the force $F$ off its application point $P$ and off its line of action and transfer the force the point $Q$. But to keep things equivalent, a couple (two equal magnitude forces, oppositely directed separated by distance $PQ$) must be added. The couple produces a pure moment, i.e. a nonzero moment that does not depend on the reference point (called pole). The new system (a force + a couple) is equivalent to the original one (single force $F$ located at $P$).
Let's contextualize this discussion to an airfoil and its the pitching moment:
The force is the lift force $L$ which acts at the point $CP$ located a distance $x_{CP}$ from the airfoil leading edge $LE$ for a specific AoA. It is mathematically possible to move the resultant lift force $L$ from $CP$ to the quarter point $AC$ located at $x_{AC}$ but we need to add a pure moment (couple force system) to keep the physics equivalent. The net pitching moment about $AC$ is just the pure moment due to the couple since the force $L$ exerts zero torque about $AC$ (zero lever arm).
Interestingly, as we change (for ex. increase) the AoA, the magnitude of $L$ increases and the distance $x_{AC}$ decreases getting closer to the $LE$. We can even in this case transfer the force $L$ to the point $AC$ along the chord (zero torque due to $L$ about $AC$) and add the pure moment. This moment will be CONSTANT and exactly the same as the pure moment for larger or smaller angles of attack. Why? Because even if the two forces in the couple are larger, their mutual distance gets smaller for a larger AoA keeping the overall pure moment the same.
Is that correct?
If we then shift the AoA to the zero-lift point, then $F=0$, leaving us with the force couple only and the same pure moment (which is the sum of all the remaining forces along the chord which balance at this angle of attack) that existed for all other angles of attack.
As long as we define the reference point to be the quarter point $AC$, all variations in lift $L$ with AoA have no moment around this point. If, however, we choose some other point as your reference point, the change in the lift force with angle of attack will add a moment, so your pitching moment is some constant value plus an angle-of-attack-dependent contribution.
Experimentally, when building a force balance that measures lift and the pitching moment using two load cells, I envision using two vertical supports attached to the wing and connected to load cells. For a certain AoA, the lift force will be given by the vector addition of the two forces, $L_{total}=F_1 +F_2$ recorded by the two load cells connected to the supports (I think).

But how would we measure the pitching moment? Where should the two supports be connected under the wing to calculate the pitching moment? How far should the supports be from each other? Essentially, how would I use the forces $F_1$ and $F_2$ to measure the pitching moment?
I think it could work this way but I need some validation: Considering the reference point to be the quarter point $AC$, the two forces $F_1$ and $F_2$ and their torques about $AC$ can be made equivalent to a single force $L_{total}$, the total lift $L_{total}$ passing through $AC$ and generating zero moment, and a single couple producing the nonzero pure pitching moment. For different angles of attack, this pure pitching moment "should" be the same...Will it?
Thanks!

There are better physicists than I at this site, but seem to remember a solution proposed in a wind tunnel test with load cells as follows:  Do the measurements separately.
Lift could be measured at the center of lift using only support 1.  C lift could vary with AOA (data points are generated one at a time from C lift at a given AOA).
Pitching moments could be measured using support 2 only, with the wing pivoting on its AC
(which could be some type of axle).


text:
Aerodynamics moment of a wing
An old flight book that I am reading discusses the aerodynamic moment about a wing and talks about an upper and lower lifts. I can see how the pressure distribution on the top surface produces an upper lift force while the the pressure distribution on the bottom surface produces also a lower lift force. The upper lift force points upward while the lower lift surface points downward. Both lift forces point away from the respective surfaces.
Wouldn't local forces (whose vector sum produces the upper lift force) due to upper pressure distribution point towards the surface, not away, in the normal direction?
As the angle of attack is increased, the upper surface lift increases while the lower surface lift decreases?
It is said that no change in moment takes place about the point where
the lift change occurs. I am not sure how to interpret that either...

What is the book?

I'm not sure it's very useful to consider the 'upper' and 'lower' lifts in order to determine the moments. It's good and in some cases useful to have a mental picture of pressure distribution above/below the wing, but when talking about integral things like moments, it's better to consider lift as an overall phenomenon for the wing.
The lift theory predicts that the overall centre of pressure will move linearly with the angle of attack (for small (pre-stall) angles, of course). It is this fact that allows us to define a point at which the moment does not change with AoA (and call it Aerodynamic Centre, AC). By doing this, we mentally decompose lift into a 'constant' part at one location and an AoA-dependent part at another (the AC) location. But always remember this is just a mental model; it is not really correct to say that the lift change actually happens at AC.
The phrase "no change in moment takes place about the point where the lift change occurs" as such is a tautology: this is so by definition. The question can only be "how can such a point exist?"
If you dig a bit more into the potential flow theory, you can find a physical explanation of this. Here decomposition of the airfoil (or rather, its lift) in to the 'camber' part and the 'AoA' part is useful. Briefly, the theory says that the centre of pressure (CP) of the camber part is fixed (and determined only by the camber); it is typically close to the middle of the chord. And the CP of the AoA-dependent part is also fixed (at about 1/4 chord), because the picture of its pressure distribution is similar: it just scales up and down. As a result, airfoils behave quite linearly with respect to AoA. But it's not easy to get it just by looking at the picture of the upper and lower pressure distributions as in your pictures.

The lower surface lift vector points downwards in the diagram, not upwards.  The nett lift is the sum of the two lift vectors, and since the lower surface lift vector is opposite to the upper, nett lift is upper surface lift minus lower surface lift.
The nett lift points upwards in the top figure, as the upper surface lift is greater than the lower surface lift.
In the middle diagram, both upper and lower surfaces have the same lift magnitude so the nett lift is zero.  Note that the chord line of the symmetric airfoil is parallel to the airflow.  This wing section has zero angle of attack (angle between the airflow and the chord line), so both the upper and lower surfaces have the same angle of attack and generate the same lift, cancelling each other out.  On the cambered airfoil, the angle of attack is slightly negative for zero nett lift.  This is because the camber causes the upper surface to generate more lift than the lower surface for a given AoA.
In the lower diagram, the upper surface has an increased angle of attack, while the lower surface has a decreased angle of attack.  So the lift of the upper surface is increased and that of the lower surface is decreased, and the nett lift is upward.
Note that the terms "up" and "down" have to be used carefully, since we usually use those terms in the context of gravity.  A lift-producing airfoil has no concept of gravity, only of angle of attack.  The airfoils in the diagram would produce the same lift with respect to the angle of attack regardless of the orientation of the airfoil with respect to gravity.  If you turned any of these diagrams upside down, the airfoils would produce exactly the same lift with respect to the surface as they did in the original ("upright") orientation.

May seem strange to talk about the lower part of the wing producing "lift" towards the ground, but this is exactly what its curved surfaces are doing at lower AoA relative to the airflow.  Note that if you invert the wing, these forces will remain the same if the AoA does not change!  Symmetrical wings are found on many aerobatic aircraft.
The gist of the diagrams is that cambered airfoils start producing lift at a lower AOA than symmetrical airfoils.  This information can be readily obtained by looking at polar graphs at Airfoil Tools on the internet, which show lift and drag properties for the entire range of AOA (from stall at negative AOA to stall at positive AOA).
Learning to read polars will be greatly beneficial in evaluating airfoil properties and for comparitive purposes.
As far as where the center of pressure (net lift) of the wing will be for a given AOA, the general rule of thumb is that it will move towards the leading edge as AOA increases.
But keep in mind as AoA increases, the horizontal stabilizer will begin to have positive lift as well.  So the TOTAL NET LIFT of the aircraft determines where the center of pressure is, not just the wing net lift contribution.
As far as showing the net center of lift moving REARWARDS as the cambered wing moves from negative AOA to zero AOA, well, it is an old book.  Use it as a mental exercise to understand net lift.  They seem to be saying the center of pressure shifts less with a symmetrical wing as AoA changes.  But don't forget the tail!

This discussion is for the wing alone to say that the total pitching moment  M_O about a specific ref. point O on the chord for a positively cambered wing can be decomposed as M_O = M_camber +M_lift where M_camber is a constant pure aerodynamic moment, solely due to camber and always present regardless of AoA and lift) and M_lift is a moment linearly depending on the lift L. If the reference point O= AC (aerodynamic center), the overall moment M_O=M_AC=M_camber and does not vary with AoA. Assuming the lift force L is applied at CP, I am still not clear why M_lift=0 when O=AC

From a practical point of view, pitching moments are determined by Cpressure and Ggravity.  Pitching "moments"  would be relative to CG.  AC of a wing (and of the whole aircraft)  is more useful to determine directional stability when compared to position of CG.  Actual pitching moments relative to AOA are best tested in the wind tunnel, and CP shift with AOA should be included in polar data!  I'm not quite buying "M camber is a constant pure aerodynamic moment", and as far as I know (in theory) change in AOA around AC does not create a pitching moment.


text:
What is the name of the profession that makes RTOW charts?
What is the name of the profession an aerodrome operator would need if they wanted to make an aerodrome RTOW (Regulatory Takeoff Weight) chart for a specific aircraft?
I've researched and found some companies who developed a takeoff chart specifically for a Falcon 10 at Canberra in the past but haven't been able to identify the name of the profession who actually build the charts. Any help would be really appreciated.

"name of the profession" seems like an XY problem. Is the real question "How can I get an RTOW chart for my aerodrome?"?

I bet the answer will ve along the lines of the answer to the question about "who uses the chainsaw in an infantry platoon?" Quite surprisingly the answer is "whoever can".

It's probably a type of aerospace engineer, or aeronautics engineer...

It's usually rather the aircraft operator or their contractor who calculates these charts, rather than the aerodrome operator. This is due to some of the required input data only known to the aircraft operator (e.g. aircraft/engine configuration, performance relevant standard procedures like V1 policy or minimum turn height etc.). The profession is most commonly referred to as Aircraft Performance Engineer, sometimes just Performance Engineer, or more generally Flight Operations Engineer.
Unfortunately I can't find decent public sources to back my (very substantiated but unproven...) claim other than loads of job offers, I'm afraid.


text:
Is it possible to graduate from ADFA and then apply for an airline job?
I am a current year 10 student wanting to become a pilot. I am choosing between going to ADFA (Australian Defence Force Academy) to take a course in aviation and the airforce fast jet pilot and going to UNSW (University of New South Wales) to take a course in aviation. I am wondering if it is ok to graduate from ADFA and then apply for an airline company straight away without doing extra studies nor licenses because I have heard that earning the license requires lots of money. If I go to ADFA and then apply for an airline would I be wasting time and money?

My advice would be to join the military only if you are eager to serve in any capacity. There are no guarantees, you could graduate from the academy and end up running a supply depot for 8 years.

In the US, the military academies expect a certain minimum military commitment (years) after graduation. You may want to check to see if the ADFA also requires a long term military commitment, then decide if you're willing to serve your country that long before deciding that it's one of your educational options. (The US MAs are also very selective, and it often takes recommendations from state or federal legislators to gain acceptance - it may be different in Aus.)

@FreeMan The answer is no. While ADFA is nominally for military personnel, like the US military academies, certain courses of study are open to civilians.

@user71659 interesting info, thanks for sharing!

Hi Anna, can you please clarify whether you are thinking of joining the Fast Jet Pilot (FJP) program, and doing so think you will gain a licence that will enable you to function as an airline transport pilot, or at least get some benefit from FJP towards ATPL?

Whichever route you choose you'll end up having to get type certificates at the very least. Historically the airline would pay for those but ever more airlines won't hire pilots unless they already have them (given the glut of airline pilots on the market after the massive scaledowns of many airlines and downright closures of others the last few years that's to be expected, but it was going on longer than that).
As the military won't teach you to fly a B777 or A320 (for example, few militaries exempted where you might end up in a special flight flying VIP transports, but those are usually very senior pilots with decades of experience, not a green as grass hiree who's only looking at the air force as a free learning experience for a future airline job).
And of course if you do go the military route you're not at all guaranteed a flying job. You sign up for the air force, the air force decides what you're going to do, and it may well end up deciding that you're better suited to be a security guard or truck driver rather than a fast jet pilot (a job that won't give you the experience or certificates needed to fly an airliner anyway, and in many air forces these days won't even give you the hours required to keep your PPL current, many air force pilots ending up renting or buying light aircraft with their own money to get those hours up).
Used to be your best job to get into the airlines would be transport pilot or flying ASW patrol aircraft. At the very least you'd have your multi engine experience. Not sure if even that is still relevant, it may be.

You won't be able to do it straight away, because the Air Force has a minimum service requirement, which for ADFA pilots is about 7 years after you've completed your training (which itself takes the length of the degree, plus about 2.5 years if you get all the way through to the fast jet program). Basically, you'll be in your  mid-30s by the time you can start to look at other jobs.
Once your minimum service is completed though you can convert your military qualifications to a civilian licence and apply for airline jobs with that. The conversion process is pretty straightforward and only costs administrative fees. So going through the military will always be cheaper, but a lot more difficult and competitive, and will take a lot longer if your ultimate goal is to get to the airlines.

Oh, don't forget, in the military, you may end up with people shooting at you. Rarely happens in a civilian flight school.

This is wrong. Certain ADFA courses of study are open to civilians. I assume the OP wants to pursue an aeronautical engineering degree because she says she isn't seeking a license.

My understanding is that there is no such thing as an ADFA pilot class anyway. Like the US you get a degree in aeronautical engineering or similar, which gives you a leg up for actual pilot training at the Air Academy.

@user71659 ?? the opening line is that she wants to become a pilot, and is considering joining the fast jet pilot course of the RAAF so I'm not sure why you assume otherwise.  The two pathways into the RAAF pilot programs are either direct-entry officer or through ADFA (which yes, is open to civilians and offers a lot more than aviation-related degrees).

@user71659 Your understanding of how ADFA works and my understanding of how it works seems to be the same. I think you got confused by my use of "ADFA pilots" - I used this because the minimum service for direct entry officers is 11.5 years (for men), but slightly different if you join via the ADFA route. It's true that there's no ADFA pilot course as such, only RAAF pilots, but as I said, one of the ways in is through ADFA.

@Ben I read the part where she says "graduate from ADFA and then apply for an airline company straight away". That makes sense. I thought she wants a civillian Bachelor's of Aeronautical Engineering and use that to join sponsored ab initio pilot training at an airline, which seems to be a reasonable path. I do see where her first statement is contradictory.


text:
Are ERA5 Pressure Level and ADS-B Geometric Height comparable?
I have two wind data sets that I want to compare:

a) Aircraft derived data (ADS-B and Mode-S).
b) ERA5 Reanalysis data.
To compare both I need altitudes to be comparable. On data set a) I have the geometric height. Precisely, it corresponds to Data Item from I021/140 from ICAO document Part 12: Category 021, as seen in the following image:

On the other hand, data set b) is given in "pressure levels". What I did is to transform this pressure level on b) to altitude using the ISA model. Then I supposed I can compare this altitude with the geometric height given on a). But I am not sure if it's correct to do so. I don't know if the pressure level on ERA5 is just a way to indicate altitudes or not.
Is it correct? If not, is there any way to compare them?
Doc.:

ERA5 reanalysis data (click here)
ERA5 model levels definition (click here)
ERA5 geometric height and pressure level (click here).
ERA5 Doc (click here and here )

Related What is the geoid undulation used for in aviation? I think you need to add the geoid undulation N to the altitude obtained from the ISA model, to get the ellipsoidal height comparable with ADS-B data. Still you'll be comparing a barometric altitude (not an actual altitude) with a GPS altitude.


text:
Can I just differentiate my Euler rates to get the angular rates?
There is this matrix:
$${W_{\eta}}=\begin{bmatrix}
-\sin(\theta) & 0 & 1 \\
\cos(\theta) \sin(\phi) & \cos(\phi) & 0 \\
\cos(\theta) \cos(\phi) & -\sin(\phi) & 0
\end{bmatrix}$$
(some other sources change the basis of this matrix so becomes mirrored). My background is robotics. When I need to find the Lagrangian (for the dynamics) I need to describe the rotational energy. This done like this: $E_{rot}=\dot{\eta}J\dot{\eta}$ where $\dot{\eta}$ is the angular velocity and $J$ is the global inertia matrix. I would have differentiated my Euler angles and call it a day. However, that is wrong.
$\dot{\eta}$ are the Euler rates and $v$ is the angular rates. And I have my Euler rates by differentiating my roll, pitch and yaw so do I have to do this to get my angular rates (source):
$ v={W_{\eta}}^T\dot{\eta}$?
Also why can't I assume Euler rates = angular rates?

If you don't get an answer here, there are also similar questions in physics like: How to compute the angular velocity from the angles of a rotation matrix?.

While the question itself is not a dup, it is, I think, fully answered here: What is the difference between Body Pitch Rate and Inertial Pitch Rate?. Basically, Euler angles (and their rates) relate to the ground, while "angular rates" (those you mean) are body angles/rates. They are just in different frames of reference. Rotation between them is not the same as for linear quantities because you need to preserve angular momentum.

@Zeus Can you explain how that matrix was obtained?

@Hamzalihi, this is exactly your matrix, inverted (to calculate Euler rates from body angular velocities, which is a more common problem in avionics, to which that question is related). Except that columns are arranged differently because of the velocity vector convention (mine is in the order of axes: [$\omega_x, \omega_y, \omega_z$], or [P, Q, R], while yours in the order of rotations: [yaw, pitch, roll]; you mention this issue re "mirrored" matrix). This matrix is not orthogonal, so it's not enough to transpose it for the opposite conversion. That's probably the source of your confusion.


text:
What does it mean when a hold short sign is out of service?
I prepared for "SELCAL" exam and in one of the routes I heard such information as

RW 32 hold short sign at TWY L is out of service.

I just don't understand this phrase. I appreciate it if someone help me.

It means that you might not be able to see the hold-short sign when you are on Taxiway L approaching Runway 32.
Perhaps the light inside the sign is not working and needs to be replaced, or perhaps the sign itself is missing because it has been run over by a snowplow.

Maybe it means that the hold short surface painted markings have faded out...but the term 'Out Of Service' I have heard applied only to lights, for example.

If the NOTAM was for faded surface markings it would say that the surface markings were faded. This is for an inop sign. Not really sure how you would think they mean the same thing.


text:
C172 alternator field circuit breaker(5a) vs alternator pull off circuit breaker(55a)
what’s the different with alt circuit breakers between 5a vs 55a??
If alt field circuit breaker pops out does that mean alternator is not producing electricity?
And if al current circuit breaker(55a) pops out does that mean alternator is producing electricity but they are just not carrying electricity to bus?
Am I correct??

please scroll down to "Advanced Regulating Systems Designs" in the reference for more info on the Voltage Regulator.

Pretty good reference here on aircraft alternator systems.  It appears the field curcuit breaker (5 amp) goes from the bus bar to the alternator to get it to start working.  Power into the bus bar is initially supplied by the battery.
Once turning, the alternator can supply all electricity needs of the aircraft, charge the battery, and keep itself running.
The alternator to bus bar breaker (60 amp) would open if excessive current was drawn from the alternator.  60 amp short curcuit would have to be a fairly catastrophic event.

Thanks for reference. As far as I understand, 5a circuit breaker acts like a overvoltage prevention. Right? when bus require more than 5a to regulator, 5a circuit breaker pops out and disconnect connection between bus and regulator which result in like shutting off Alt master switch. Am I correct??

@Jimmy. It seems to be on the same circuit as Alt master switch, but the bus provides current, something down the line is drawing too many amps.  If this is happening, I would consult a mechanic right away.  I believe the 172 can keep running on its magneto even if both alt and batt are off, but the whole bus will be dead.

@Jimmy The 5A breaker supplies power to the alternator field. Needing a little input power to make a lot of output power is a key difference between alternators and generators, and that’s what you seem to be misunderstanding.

@Jimmy, Per the linked document, overvoltage protection is yet another element. Circuit breakers always break on overcurrent.


text:
What are the A320 ECAM system displays' dimensions?
I am a student taking up an Aeronautical engineering course. We were assigned to draw A320 ECAM system pages. However, I have a difficulty finding the dimensions for each of the system pages.
What are the dimensions for the ECAM system pages?

Why not ask your professor?

Possible duplicate of: https://aviation.stackexchange.com/questions/91186/where-can-i-find-a-description-of-the-ecam-system-pages

Also see: https://aviation.stackexchange.com/questions/51333/does-the-airbus-a320-or-boeing-737-have-better-resolution-screens-in-the-cockpit
Besides individual system pages, you are probably interested in https://www.smartcockpit.com/docs/A319-320-321-Indicating_and_Recording.pdf

You’re not looking for different sizes here, each of the 12 ECAM system pages is displayed on the lower ECAM display unit (DU) so they’re all the same size.  As I recall A320 DU’s are about 160mm x 160mm but I’ll get my tape measure out when I’m sat in front of one on Monday

Personally I don’t normally use French measurements of length hence the confusion


text:
What is this aircraft seen near Farnborough almost every day?
Can anyone identify the aircraft seen almost every day making for Farnborough airfield based on this description?

medium sized aircraft
single front engine with a weird engine sound
front fins, could be stablisiers
high rear tailplane

It would really help, if you could add a picture of this aircraft.

How about taking a look at FlightRadar24 to see if you can find the aircraft on there, then, if it's there, give us a link to the flight. FR24 might tell you what kind of plane it is, but at least others would have something to start with.

I've now got my camera @ the ready for the next fly past,your comments about the Pilatus seem justified,but the one that I am seeing is almost like a canard,but with everything else in the right position,these front fins that I am seeing are almost the same as the Typhoon or Sukoi jet.Thank you for your interest.Dave.

From the description you give, and a little local knowledge, I'm going to hedge a bet that it is a Pilatus PC12

medium sized aircraft: Not very clear what "Medium size" really is, but its certainly bigger than your usual single engine aircraft, but considerably smaller than a large bizjet or airliner
single front engine with a weird engine sound: Check! It's single engine turbo prop which do sound quite considerably different to either a piston or jet engine
front fins, could be stablisiers: This one threw me a bit, but I think you may have misidentified the quite distinctive engine exhausts for fins at the front
high rear tailplane: Check! It's a pretty distinguishing feature of a PC12 not present on other similar sized aircraft

This might be the view you are familiar with if you're on the ground (c/w wikimedia commoons)

Or this one if you see it side on

The only thing which doesnt really add up is your guess that they are "Heading for Farnborough". Most of the traffic in and out of there are business jets, but Farnborough provide the lower airspace radar service for much of SE England, so it's not unual for flights to transit their airspace. Blackbushe airport is nearby, it could perhaps be heading for there, or one of the other smaller airfields surrounding London or elsewhere. Where I fly from (Elstree, about 25 miles NE of Farnborough) has 2 based there, and about another half dozen are based at Denham about 10 miles east of Elstree.

or something like a Malibu, or a TBM, or or or or...

@jwenting none of the TBM that I can think of or find have a high tailplane as I mentioned in the answer.  Nor does a malibu.